(a) Field of the Invention
This invention relates to an image posture converting optical system to be used for microscopes, optical measuring instruments and the like.
(b) Description of the Prior Art
An optical system for variously bending a light path by combining prisms is used for microscopes and optical measuring instruments. In case such optical system is used as an optical system for conducting a light from an objective to a eyepiece, for example, in a microscope, depending on the manner of arranging the prisms, the image will rotate within the visual field of the eyepiece.
A method used conventionally to keep a correct image posture by correcting such rotation of the image has been to rotate by a proper angle an image rotator arranged in a proper position within a light path. In other words, in the prior art, to compensate for the fact that the image as viewed at the eye piece may have a different angular orientation than actual subject matter upon which the optical system is trained, it is conventional to incorporate in the optical system as a distinct element an image rotator, i.e. an element which can be manipulated simply to adjust the angular orientation of the image as viewed at the eye piece until it matches the angular orientation of the actual subject matter being viewed.
However, in such a method, the image rotator is separate from the prisms and reflecting surfaces required to bend the light path and therefore there are defects that the optical system is complicated to manufacture and is large in size. For example, such image rotators as are shown in FIGS. 1 to 3 are provided in the prior art. In the prism in FIG. 1, it is necessary that the light bundle entering the prism should be a parallel light bundle and therefore manufacture of the optical system is complicated. Also, in the prism in FIG. 2, there is a drawback that the prism is so large as to be hard to use. Further, the prism in FIG. 3 has as many as five reflecting surfaces and therefore has a drawback that the optical performance deteriorates.